Displacement
FP Reference Points
Description
A "FP" was not an electronic sensor, but a reference point used to periodically quantify frost heave of a pavement surface layer.There were two types of Frost Pin (FP) reference points. One consisted of small steel rods installed into the surface of test cells (sunken so tires and snowplow blades could not damage or move them). The other type consisted of a steel rod (reaching to just below the pavement surface) mounted on top of a square plate installed into a particular subsurface layer. Periodic elevation measurements were taken by placing a survey rod on top of the frost pins.
Manufacturer
The frost pins were designed and fabricated by MnROAD staff.
Location and Quantity
Frost Pins were originally placed in several test cells to allow characterization of frost heave in various surface and subsurface layers.
Current Status
Frost pin measurements were discontinued in spring 1997. F. MnROAD Database Table i. Data from frost pins can be found in the MnROAD database table: MNR.FP_VALUES.
Concrete Joint Opening Horizontal Clip - HC
Description
A "HC" sensor measures the opening and closing of a PCC transverse contraction joint due to environmental forces. Data is automatically collected once every 15 minutes, due to the slow rate of change of the movement.
Description
The Horizontal Clip (HC) sensor is a U-shaped strip of metal to which strain gauges are mounted. As the strip of metal is flexed, measured strain in the metal strip is converted to represent the displacement (separation) of the two legs of the device. Each leg of the sensor is mounted to span across a transverse PCC joint.
Manufacturer
Tokyo Sokki model TML PI-5.
Location and Quantity
HC sensors were originally mounted within large holes, spanning across transverse joints, blocked out during the paving of the concrete slabs. Following installation of the sensors, a split steel cover, with a rubber disk underneath, was bolted to the surface to allow for movement of the joint and to provide protection to the 6 sensor. A modified installation procedure was implemented in 2000.
There were originally 80 HC sensors located in 14 MnROAD PCC test cells. Newer PCC test cells at the MnROAD facility have also included the installation of Tokyo Sokki model PI-5 sensors.
Current Status
The original sensors performed very well for approximately 4 years, at which time the original mounting systems began to fail (rusted brackets or sand infiltration from the base below). The improved mounting technique appears to be performing for a longer period of time. Original (1993) sensors have been removed, but newer (2000) installations are still functioning.
MnROAD Database Table
Data has been collected automatically every 15 minutes over the life of each sensor. Data can be found in MnROAD database tables: Displacement=MNR.HC_VALUES; Raw voltage from sensor=MNR.HV_VALUES.
Tiltmeter - TT/TL
Description
A "TL" or "TT" sensor measures the slope of a PCC slab in the direction in the direction of traffic. Data is automatically collected once every 15 minutes, due to the slow rate of change of the movement. The Tiltmeter (TT/TL) sensor uses precision electrolytic transducers to detect angular motion in two perpendicular directions. The transducers operate on the fundamental principle that a bubble suspended in a liquid-filled case, is always bisected by a vertical gravity vector. As the transducer tilts, the case moves around the bubble, linearly changing the electrical resistance measured through the electrolyte. Internally, there are two sensors, one oriented longitudinally(TL) and one transversely(TT) to traffic.
Manufacturer
Applied Geomechanics model 756-1129 Mid-range Miniature Tilt Sensor.
Location and Quantity
TT/TL sensors were mounted in one panel within test cell 39. The sensors were placed on top of a flat plate placed on the base, and paved over with the PCC, to become embedded near the bottom of the slab.
There are 15 TT/TL sensors (15 TL and 15 TT) located in MnROAD PCC test cell 39. E. Current Status 7 i. Performance of the TT/TL sensor has been very good. All 15 sensors appear to continue to function.
MnROAD Database Table
Data has been collected automatically every 15 minutes over the life of each sensor. Data can be found in MnROAD database tables: MNR.TL_VALUES, MNR.TT_VALUES.